1. Field of the Invention
The present invention relates to an upper support for a car radiator which elastically holds the radiator at the radiator top in cooperation with a lower support at the radiator bottom.
2. Description of the Prior Art
A car radiator is supported on a car body by means of an upper support and a lower support which have rubber members to adjust the dimensional errors in assembly and to absorb a thermal expansion difference between the radiator support assembly and the car body. Such a structure for radiator support constitutes a vibrational system which has the radiator mass, including the mass of the engine-cooling water, in the radiator and the spring constants of the rubber members in the upper and lower supports. The natural frequency of this vibrational system should be carefully set such that it will not aggravate an idle vibration of the engine or induce or aggravate the internal car noise.
FIG. 1 shows the upper support for the radiator which was proposed in Japanese Utility Model Application No. SHO 58-60810, yet to be published.
As illustrated in FIG. 1, the proposed upper support for the radiator consists of a body bracket 1 to be fitted to the car body and a radiator bracket 2 to be in pressure-contact with the radiator. The brackets 1 and 2 are joined together by a rubber member 6 which has right and left rubber props 3, 4 inclined downward from the body bracket 1 toward the radiator bracket 2 with a cavity 5 positioned between said props 3 and 4.
In the above structure of the radiator upper support, the dimensional errors in the assembled radiator as well as the thermal expansion produced therein are absorbed by the elastic deformation of rubber props 3, 4, and accordingly by the dimensional changes made in the bored cavity 5 in the upward and downward direction.
The structure of the upper support illustrated in FIG. 1 has been changed in a variety of ways to investigate the changes in its vibrational characteristics, particularly its spring constant, with a view toward providing good vibration suppressing characteristics in addition to its dimensional error-absorbing capacity. The results are summarized in FIG. 2. In FIG. 2 in which the abscissa is the initial compression in an assembled radiator, i.e., the change in the upward-downward dimension D of the cavity 5 in FIG. 1 and the ordinate is the dynamic spring constant of the upper support, the curve A represents the relation between the dynamic spring constant and the dimension D of the bored cavity of the conventional upper support in FIG. 1.
As evident from FIG. 2, the dynamic spring constant of the upper support which has its rubber props disposed in a V-shaped fashion after radiator assembly is highly sensitive to a change in the upward-downward dimension of the bored cavity due to a dimensional error in the assembled radiator, or to a change in the thermal expansion of the radiator. In FIG. 2, W indicates the range of variations in the upward-downward dimension of the bored cavity 5 due to assembly errors and/or errors created by the thermal expansion of the radiator.
In the large dimension part of the range W the force acting on the rubber props 3, 4 is mainly compression and accordingly the props exhibit a high value of the dynamic spring constant. In the small dimension part of the range W the force acting on the props 3,4 is mainly bending and accordingly the props exhibit a low value of the dynamic spring constant. Thus the dynamic spring constant fluctuates widely with variations in the upward-downward dimension of the bored cavity 5. Meanwhile, there must be a part in the range of the dynamic spring constant which would effectively contribute to suppression of an idle vibration of an engine or internal car noise. When such a part is indicated by H, the portion of the curve A which deviates from this effective range H of the dynamic spring constant, i.e., the portion A.sub.1 may be called that portion which is likely to aggravate the idle vibration or the internal car noise. Thus there will be no problem when the radiator has been assembled with high precision and the dimension of the bored cavity falls within the range W.sub.1, which corresponds to the effective range H of the dynamic spring constant. But when the dimension of the bored cavity falls outside of the range W.sub.1 in the range W, in other words, falls within the part A.sub.1 of the curve A, then the idle vibration and the internal car noise are likely to be aggravated.